Method of producing fired ceramic blocks



PAUL G. WILLETTS, OF WEST HARTFORD, CONNECTICUT, ASSIGNOR TO HARTFORD-EMPIRE COMPANY, OF HARTFORD, CONNECTICUT, A CORPORATION OF DELAWARE.

METHOD OF PRODUCING FIRED CERAMIC BLOCKS.

No Drawing.

My invention relates to the manufacture, by ceramic methods, ofrefractory blocks such as flux blocks for glass furnaces. Its object isto provide an improved process of controlling the-shape of such blocksso that they shall have opposite sides of equal dimensions,notwithstanding a tendency to unequal dimensional changes which resultsfrom the method .by which the blocks are manufactured.

The present invention is appurtenant to a new system which I havedeveloped for making refractory bodies by ceramic methods. In thissystem,'clays and other selected ingredients are combined in the properproportions to produce, by chemical rearrangement when the bodies arefired in their final form, a dense, homogeneous and finely grainedmaterial, typically consisting of mullite and a small amount of vitreousslag. The temperatures which I employ for firing these bodies frequentlyexceed 3000 F. At these temperatures the transforming reaction takesplace quickly and within a comparatively narrow range of temperature,and the material begins to lose its rigidity to a very slight extent.

These refractories are unusual, not only in their chemical and physicalstructure but also in the fact that they tend to shrink unequally duringthe firing operation. Thus when a rectangular block of considerablesize, such as 9x9x4 inches, is fired at "such high temperature upon anordinary pallet after being made by the process outlined above, or byany-other ceramic process in which the block begins to loseits rigidityduring firing,th e portion of the block adjacent to the pallet shrinksless than the portions which are further removed from the pallet duringthe firing operation.

Therefore, a block that is perfectlyrectangu-- lar when placed in thekiln will be sub stantially smaller at its upper endthan at its lowerend when the firing is complete, the lower end of the block beinglocally enlarged or" ared outwardly. Such irregular blocks areundesirable for building the walls of glass furnaces? and for other useswhere the blocks shouldbe laid closely together. Y

The reduced shrinkage at the bottom of the block appears not to bemerely the result of slumping throu h softening. Itlmay be a result ofthe frictional resistance to shrinking ofiered by the support on whichApplication filed September 23, 1926. Serial No. 137,388.

block, or it may be due to difference in the absorption of heat by thetop and bottom of the block causing chemicalconversion of tem . the topand bottom to take place at different stages of shrinkage.

My present invention aims to cause equal shrinkage at the top of such ablock and at the bottom of the block on which it rests during firing. Tothis end, I prepare the itself shrink, during firing, at least as muchas the blocks themselves. The blocks are then fired in the usual manner,but preferably in one course only, the blocks not being stacked upon oneanother. After the firing operation they will be found to have shrunkequally at the top and bottom surfaces. The shrinkage of the supportavoids any resistance to the shrinkage of the bottom of the block, andif the support shrinks more than the block, there may be an actualcompressive stress exerted upon the block by the support.

Numerous materials are suitable for use as the supports for the blocksduring firing. For example, such supports may be; made of an unburnedgrog mixture such as I have described in my co-pending application. forLetters Patent filed March 1, 1926, Serial No. 91,361. A supportingpallet made from one of the "raw mixtures described in my copen'dingapplication Serial No. 91361. may have a shrinkage of about 7 while theblocks, if made according to the disclosure .of the same application,may have a shrinkage of about 5%. I prefer to use such a raw mixture orsome other material which, after burning, may .be broken up and used asgrog or otherwise,- since such procedure avoids wasting the material ofwhich the supports are composed. If desired, the su v- 7 ports for theblocks may be composed of.th e

same material from which the blocks themselves are made.

Powdered or granular refractory material may be interposed between thesupports and the blocks during firing,.in-orde r to insure i that theblocks'will not stick to the supports. Such material may be-powdered orcrushed alundurmor fired and crushed material lar to the aterialcomposing the pellets. The interposed material may or may not shrinkduring firing. I

I am aware that refractory bodieshave been stacked upon one another forfiring, but in all suchcases known to me, such refractory bodies havenot been subject to the dimensional changes which tend to occur when therefractory-material is brought to such temperature in the that it beginsto lose rigidity. Therefore, I consider that such dimensional changespresent a new prohiem, particularly since it has. never been thepractice heretofore to burn to maturity refractory blocks of substantialsize. invention is'also guished from prior processes: in which blockshave been stacked upon one another for firing, by the fact each blockrests firmg upon a support which is discarded or is used otherwise thanas a block, whereas in the ordinary processes, blocks are intended foruse as such. In carrying out the present invention, the blocks cannot bestacked upon one another for because 1 the lower course or courses ofblocks. would be deformed as pointed out above, and, in-

' material, which support,

addition, the lower hlocks.would be de formed still more by'the weightof the upper blocks.

I claim as my invention l. The method of producing a fired ceramic blocksubstantially equal opposhrink at least as much as said block, and

subjecting-said block and said supportto a firing temperature suflicientto cause said block to tend to shrink unequally at top and bottom."

3; The-method of producing a fired ceramic block ha etilual oppositefacesffrom material which, w en heated to maturity on a rigid support,tends to shrink less near its lower face than in its 7 per portions,which method comprises u pacing the block upon a sup rt of mate which,duringfring, will at least as much as said l and subjecting-said blockand said support to a temperature suflicient to mature said block.

4. The method of producing a fired ce ramic block having substantiallyequal opposits faces, from material which, when heated to maturity on a.rigid support,;tends to shrink less near its lower face than in its Iupper portions, which method comprises placing the block upon a layer ofgranular or powdered refractory material on 2: support ofrefractorymaterial, which support, during firing, will shrink at leastas much as said block, and subjecting said block and said support to atemperature sufficient to V mature said block.

ceramic equal ppo 5. The method of blocks, having substantially faces,from material which when heated to maturity on a rigid support tends .toshrink less near its lower face than in its upper portions, which methodcomprises the steps of placing the block for firing upon a supportcomposed of material entering into the composition of the said block,which support, during firing, will shrink at least as much as saidblock, subjecting said block and said support to a temperature at whichshrinkage occurs in both'the block and support, and thereafter removingthe burned block and using the burned support in the manufacture ofother similar blocks.

Signed at Hartford, Connecticut, this 22nd day of September, 1926.

PAUL G. WILLETIS.

